Reproductive performance of Merino ewes grazing red clover (Trifolium pratense L.), improved pasture, or native pasture

Barrett, JF; George, JM; Lamond,

doi:10.1071/ar9650189

Cited by 30 publications

(12 citation statements)

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“…In contrast, we found that grazing red clover did not affect the incidence of oestrus over the mating period, a finding supported by Newton & Betts (1973). Barrett et al (1965), using the opposite grazing regime to ours (i.e. ewes grazed red clover pasture during pregnancy and lactation), did not record any differences in conception to first service, but did note an increase in barrenness.…”

Section: Discussioncontrasting

confidence: 73%

Effects of prolonged exposure of ewes to oestrogenic pasture 1. Permanent flock infertility following long-term grazing of red clover (‘Grasslands Pawera’)-dominant pasture

Shackell

Kelly

Johnstone

1993

New Zealand Journal of Agricultural Research

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Romney ewes grazed red clover (P) or mixed red clover/ryegrass (M) pastures for about 6 months/year until mating in Year 4 (P) or 5 (M) of a 6-year study. A further group grazed ryegrass/ white clover (C) pasture continuously throughout the study. At other times all animals grazed ryegrass/white clover pasture as one mob. Ewes grazing P pasture were consistently 3-6 kg heavier than ewes that grazed C pasture. Despite similar proportions of ewes being marked by the ram, and similar ovulation rates, during the first cycle of mating each year, ewes grazing P pastures consistently showed increased returns to service (+30%), increased barrenness (+30%), and fewer lambs born per ewe joined (-0.5) than ewes grazing C pasture. Differences persisted after ewes were removed from treatment pastures, indicating that infertility was likely to be permanent.

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Section: Discussioncontrasting

confidence: 73%

Effects of prolonged exposure of ewes to oestrogenic pasture 1. Permanent flock infertility following long-term grazing of red clover (‘Grasslands Pawera’)-dominant pasture

Shackell

Kelly

Johnstone

1993

New Zealand Journal of Agricultural Research

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“…When grazed at or about mating, conception rates and ovulation rates (or lambs born per ewe lambing) are decreased (Morley et al 1964;Newton & Betts 1973;Lightfoot & Wroth 1974). Permanent and progressive infertility occurs when formononetin-rich pastures are grazed for prolonged periods at any time of the year (Barrett et al 1965;Davenport 1967;Davies & Maller 1970). There is also some evidence to suggest that if ewe lambs graze oestrogenic clovers, their subsequent fertility may be affected (Underwood & Shier 1951;Marshall 1973), although Ch 'ang (1961 found no carryover effects.…”

Section: Haymentioning

confidence: 99%

Formononetin content of ‘Grasslands Pawera’ red clover and its oestrogenic activity to sheep

Kelly¹,

Hay²,

Shackell³

1979

New Zealand Journal of Experimental Agriculture

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“…Long-term grazing of oestrogenic clover pastures may cause permanent infertility in ewes (Bennetts et al 1946;Barrett et al 1965) although not all ewes grazing oestrogenic clover exhibit infertility. Infertile ewes have uterine endometrial hyperplasia and changes in cell type and function of the cervix (Adams 1976).…”

Section: Introductionmentioning

confidence: 99%

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

Rodgers

Clarke

Findlay

et al. 1980

Aust. Jnl. Of Bio. Sci.

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The levels of plasma LH and FSH were measured in serial blood samples taken at 15-min intervals for 6 h from ewes that had remained fertile after grazing oestrogenic pasture (clover-fertile ewes), from ewes that were permanently affected by clover disease (clover-infertile ewes) and from normal ewes. Two flocks of ewes from different locations were studied. In flock I, tonic LH secretion (total area under the curve of LH concentration versus time, 1 area unit = 1 ng ml-1 x 1 h) was significantly (P < 0'05) greater in clover-infertile ewes (10'4 area units) during anoestrus than in ewes that had remained fertile after prolonged grazing of oestrogenic clover (5·4 area units). Tonic LH and FSH secretions during the breeding season and FSH secretion during anoestrus were not significantly different. In flock 2, LH levels during the breeding season were significantly (P < 0'05) elevated in clover-infertile ewes (10' 9 area units) compared to normal ewes (5' 4 area units) that had never grazed oestrogenic clover. LH secretion in clover-infertile ewes (7. 8 area units) was intermediate to that found in infertile and control ewes. Concentrations of FSH, progesterone and ovarian vein oestradiol-17 P (Ez) during the breeding season were similar in the three groups.In another experiment, the positive feedback release of LH following administration of Ez (12'5,25 or 50 f.1g per ewe) was measured in anoestrous ewes of flock 2. Significantly (P < 0·01) more clover-infertile ewes demonstrated a positive feedback effect than control ewes when given 12· 5 f.1g Ez but not when given higher doses.The elevation of LH secretion in permanently affected clover-infertile ewes is consistent with the hypothesis that the hypothalamo-pituitary axis of these ewes is less responsive to the negative feedback effect of oestrogen. Furthermore, the patency of the positive feedback loop is consistent with the ability to ovulate.Other keywords: Clover disease. IntroductionLong-term grazing of oestrogenic clover pastures may cause permanent infertility in ewes (Bennetts et al. 1946;Barrett et al. 1965) although not all ewes grazing oestrogenic clover exhibit infertility. Infertile ewes have uterine endometrial hyperplasia and changes in cell type and function of the cervix (Adams 1976). In addition, there may be an associated neuroendocrine lesion. For example, Findlay et al. (1973) have reported that when infertile ewes which had previously grazed oestrogenic clover were ovariectomized, they were less likely to show elevated plasma LH levels, i.e. positive feedback (Goding et al. 1969), in response to oestradiol-17f1 (E 2 ) treatment than were normal ovariectomized ewes. This reduced responsiveness of the hypothalamo-pituitary axis to E2 could be related to changes in the number or affinity

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Reproductive performance of Merino ewes grazing red clover (Trifolium pratense L.), improved pasture, or native pasture

Cited by 30 publications

References 0 publications

Effects of prolonged exposure of ewes to oestrogenic pasture 1. Permanent flock infertility following long-term grazing of red clover (‘Grasslands Pawera’)-dominant pasture

Effects of prolonged exposure of ewes to oestrogenic pasture 1. Permanent flock infertility following long-term grazing of red clover (‘Grasslands Pawera’)-dominant pasture

Formononetin content of ‘Grasslands Pawera’ red clover and its oestrogenic activity to sheep

Plasma LH and FSH in Ewes That Were Either Fertile or Infertile After Long-Term Grazing of Oestrogenic Pasture

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